Which process in the light reactions of photosynthesis is most directly driven by light energy?

• A. Synthesis of glucose from carbon dioxide
• B. Formation of ATP from ADP and inorganic phosphate
• C. Reduction of NADP^+ to NADPH
• D. Excitation of electrons in chlorophyll molecules

Answer: (D)

Verified step by step guidance

1. Understand that the light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts and are driven by light energy.
2. Recognize that light energy is absorbed by chlorophyll molecules in photosystems (Photosystem II and Photosystem I). This absorption excites electrons in the chlorophyll molecules to a higher energy state.
3. Note that the excitation of electrons is the initial step in the light reactions and is directly driven by light energy. This process is essential for the subsequent steps in the light reactions.
4. Understand that the excited electrons are transferred through an electron transport chain, which leads to the production of ATP and the reduction of NADP⁺ to NADPH. However, these processes are indirectly driven by light energy.
5. Conclude that the excitation of electrons in chlorophyll molecules is the process most directly driven by light energy, as it is the first and primary event triggered by the absorption of light.